Heated frying oils with different chemical properties in terms of AV (acid value), POV (peroxide value), COV (carbonyl value), and contents of polar compounds (PC) and triacylglycerol (TG), as well as color and odor, were obtained. Male Wistar rats were fed ad libitum for 12 weeks a powdered diet (AIN93G; no fat) containing 7 wt% of fresh oil (control) or one of the frying oils described above. The rats were subjected to anthropometric measurements, hematological analyses, and observations of the liver and kidneys. All of the rats grew well, and no gross symptoms attributable to the experimental oils were observed. However, the rats fed a diet containing the heated oil developed apparent liver damage to different degrees regardless of the chemical properties of the ingested oils. Thus, it was suggested that the chemical properties evaluated here had little to do with the cytotoxicity of heated oil, although the properties express quality of oil. Volatile compounds seem to be major candidates for the toxic agents in heated oil because oils with rancid and deteriorated odor show strong toxicity.